Re: day 3000 of 3rd

Reed, Sir:
>.....Needs a catchy name. :)During this International Astronomy Year 2009, PERHAPS! Yes, today is 78th day after 8 years during this millenium, marking 3000th day.
I take liberty of attachment of my proposed World calendar for UN consideration, as my documents point to its need vs advocacy.Brij Bhushan Vij

Vernal Equinox Re: day 3000 of 3rd

It is? According to timeanddate.com, the 3000th day of the
3rd millennium is on 2009.03.20-Fr, so you're off behind by one day. The Vernal
equinox will also fall on that day at 11:43:22 GMT (07:43:22 EDT) according to
Kalendis where the sun londitude will be at 0.0°. For my
location, Tilbury, Ontario, Canada, the local mean time will be at 06:13:39,
while the local appearant time will be 06:06 on that date and time.

Re: Vernal Equinox Re: day 3000 of 3rd

No, Irv is right. If day 1 of the third millennium was January 1st,
2001, then today, March 19th, 2009, is day 3000.

I imagine the error on timeanddate.com comes from assigning day number
zero to January 1st, 2001, in which case day number 3000 is tomorrow.
But even if you consider today to be day number 2999 in a zero-based
count, that's still the 3000th day!

Even if you don't have recourse to a JD or RD calculator, it's not
hard to tally up:

Vernal Equinox RE: Vernal Equinox Re: day 3000 of 3rd

Irv, Reed sirs:
>.....assigning day number>zero to January 1st, 2001, in which case day number 3000 is tomorrow.
Vernal equinox that is generally taken to be on March 21st 'possibly need be aligned' on March 19th i.e. today as *a correction of TWO days to Gregorian calendar*. Doing some calculation for 3000th day:
3000 days =3000/365.2421896669781 =8 years 78 days 1h 49md 96sd.
Counting from mid night 1999 Dec.31st./2000 Jan.01st, the day 3000th has already past 78 days after 8 years, as such this IS 3001st after midnight 2009 March 19th.
Irv is right, I guess! Kalendis and other software may speak any language.
However, Vernal Equinox is the point in time when SUN is directly over head and causing EQUAL 12-hours in TWO hemispheres of Earth.
Regards,Brij Bhushan Vij

Re: Vernal Equinox Re: day 3000 of 3rd

Sunrise and sunset are defined as the moment when the _upper_edge_ of the sun
disk is at the horizon. In the Netherlands, last Wednesday was the day when
day and night had equal length.

The vernal equinox is defined only by the heliocentric ecliptic longitude of
earth being zero. The ecliptic latitude, which is not always exacly zero, is
completely ignored. Earth's nutation is also ignored, so the moment when the
sun is exactly in the equatorial plane is usually not the very same moment as
that of the vernal equinox.

> On 2009.03.19, at 19:56 , Brij Bhushan Vij wrote:
>> However, Vernal Equinox is the point in time when SUN is directly
>> over head and causing EQUAL 12-hours in TWO hemispheres of Earth.
>
> The only way that you'll reckon a 12-hour day and 12-hour night on the
> day of the vernal equinox is if you use an equatorial sundial to
> reckon the time!
> (Some other types of sundials may also yield such readings also, but
> I'm less familiar with them.)
> The ancients considered day and night equal on the day of an equinox
> because they used sundials to reckon time.
>
> If you use a clock that proceeds at the rate of mean solar time, then
> the daytime will be approximately 30 minutes longer than the nighttime.
> Daytime will be about 12h 15m, nighttime about 11h 45m.
> The exact amounts depend on the observer's latitude, and when is the
> actual moment of the equinox in relation to sunrise and sunset at the
> observer's locale.
>
> Due to atmospheric refraction, when Sun is at the horizon it appears
> to be higher than its actual geometric position.
> Also, Sun appears as a disk almost 1/2° in diameter, and it is daytime
> when any part of that disk is above the horizon.
>
> If Earth had no air, and if Sun were a bright point of light, then
> yes, on the day of an equinox the length of day and night would be
> equal.
>
> OK, so 3000 days have now ELAPSED since the beginning of the 3rd
> millennium, and the northward equinox happened about an hour ago as I
> write this...
>
>
> -- Irv Bromberg, Toronto, Canada
>
> <http://www.sym454.org/seasons/>
>
>

Re: Vernal Equinox Re: day 3000 of 3rd

On 3/20/09, Irv Bromberg <[hidden email]> wrote:
>
>
>
> On 2009.03.19, at 19:56 , Brij Bhushan Vij wrote:
>
> However, Vernal Equinox is the point in time when SUN is directly over head and causing EQUAL 12-hours in TWO hemispheres of Earth.
>
>
> The only way that you'll reckon a 12-hour day and 12-hour night on the day of the vernal equinox is if you use an equatorial sundial to reckon the time!

How do you figure? Atmospheric refraction certainly impacts sundials.

I suspect the ancients may have used another method for determining
when the equinox occurred: the angle of the path of the sun above the
horizon varies with the seasons. The maximum and minimum occur at the
solstices. Exactly half way (not in terms of time, but in terms of
angle) in between marks the equinoxes.

Re: Vernal Equinox Re: day 3000 of 3rd

The vernal equinox is defined only by the heliocentric ecliptic longitude ofearth being zero. The ecliptic latitude, which is not always exacly zero, iscompletely ignored. Earth's nutation is also ignored, so the moment when thesun is exactly in the equatorial plane is usually not the very same moment asthat of the vernal equinox.

Definitions based on celestial mechanics can be much more precise, but then one runs into controversies as to exact definitions of the moment.

Isn't the "heliocentric ecliptic longitude of earth being zero" undefined in isolation?

There is no heliocentric longitude in space which points to a fixed zero, because of precession of the equinoxes.

The only "nail to hang one's hat on" is the solar declination crossing zero, and at that moment one can define the ecliptic solar longitude as 0° at the northward equinox, corresponding to a heliocentric ecliptic longitude of Earth = 180°.

If the equinox is the moment of solar declination zero, then how can that be distinguished from a zero ecliptic latitude?

With respect to nutation in this context, it would be included in typical solar longitude calculations, but generally not in the solar declination calculation.

Irv replies: Yes, it does, but would you not be hard-pressed to read the moment of sunrise / sunset on a sundial so tight enough precision that it would make a difference?

Victor continued: I suspect the ancients may have used another method for determiningwhen the equinox occurred: the angle of the path of the sun above thehorizon varies with the seasons. The maximum and minimum occur at thesolstices. Exactly half way (not in terms of time, but in terms ofangle) in between marks the equinoxes.

Irv replies: Indeed, there is an example of that method being described in the Talmud Eruvin page 56a.

However the observation of the solstice sunrise directions are also subject to similar refraction errors, greater at higher latitudes because Sun skims along the horizon at a more acute angle, and the true maximum north-east and south-east directions of sunrise can only be seen if the moment of the north solstice and south solstice respectively both occur at the moment of sunrise at the observer's locale, and there are periodic variations of solstices and equinoxes of about ±15 minutes due mainly to the lunar cycle (with non-negligible contributions from Venus and Jupiter). (Similarly for the sunset direction.) If the positions were marked and recorded over a number of years then there is a better chance that the correct maxima will be found. These are limitations of observational techniques.

Re: Vernal Equinox Re: day 3000 of 3rd

I just had a thought. What if there could be more than two equinoxes
in a year due to notation. Well, that is probably impossible because
nutation is so small compared to the movement of the sun northward or
southward. OK. So what about the solstices? Those take place when the
north/south movement of the sun is zero.

So, for example, if we define the summer solstice as a local northern
extreme of the sun's apparent position in the sky, it seems possible
to have two such local maxima if the amplitude of the nutation is
strong enough and in the opposite direction.

>
> On 2009.03.20, at 11:00 , HR-CALNDR-L wrote:
> The vernal equinox is defined only by the heliocentric ecliptic longitude of
> earth being zero. The ecliptic latitude, which is not always exacly zero, is
> completely ignored. Earth's nutation is also ignored, so the moment when the
> sun is exactly in the equatorial plane is usually not the very same moment
> as
> that of the vernal equinox.
>
> Irv replies: My comments concerned rather crude observation of the equinox.
>
> Definitions based on celestial mechanics can be much more precise, but then
> one runs into controversies as to exact definitions of the moment.
>
> Isn't the "heliocentric ecliptic longitude of earth being zero" undefined in
> isolation?
>
> There is no heliocentric longitude in space which points to a fixed zero,
> because of precession of the equinoxes.The only "nail to hang one's hat on"
> is the solar declination crossing zero, and at that moment one can define
> the ecliptic solar longitude as 0° at the northward equinox, corresponding
> to a heliocentric ecliptic longitude of Earth = 180°.
>
> If the equinox is the moment of solar declination zero, then how can that be
> distinguished from a zero ecliptic latitude?
> With respect to nutation in this context, it would be included in typical
> solar longitude calculations, but generally not in the solar declination
> calculation.
>
>
>
> -- Irv Bromberg, Toronto, Canada
>
> <http://www.sym454.org/seasons/>

Re: Vernal Equinox Re: day 3000 of 3rd

> The only way that you'll reckon a 12-hour day and 12-hour night on the day
> of the vernal equinox is if you use an equatorial sundial to reckon the
> time!
>
>
> Victor wrote: How do you figure? Atmospheric refraction certainly impacts
> sundials.
>
> Irv replies: Yes, it does, but would you not be hard-pressed to read the
> moment of sunrise / sunset on a sundial so tight enough precision that it
> would make a difference?

Sure. You brought up the point about refraction, though. And here you
seemed to be assuming that it was not a factor. It is.

> Irv replies: Indeed, there is an example of that method being described in
> the Talmud Eruvin page 56a.
>
> However the observation of the solstice sunrise directions are also subject
> to similar refraction errors, greater at higher latitudes because Sun skims
> along the horizon at a more acute angle, and the true maximum north-east and
> south-east directions of sunrise can only be seen if the moment of the north
> solstice and south solstice respectively both occur at the moment of sunrise
> at the observer's locale, and there are periodic variations of solstices and
> equinoxes of about ±15 minutes due mainly to the lunar cycle (with
> non-negligible contributions from Venus and Jupiter). (Similarly for the
> sunset direction.) If the positions were marked and recorded over a number
> of years then there is a better chance that the correct maxima will be
> found. These are limitations of observational techniques.

True. I wasn't talking about sunrise/sunset direction, though, but
maximum elevation of the sun above the horizon -- zenith. The
northernmost zenith occurs at the northern solstice. The southernmost
zenith occurs at the southern solstice. My assertion is that the
equinox occurs at and angle that is midway between those two angles.
These angles are related to sunrise and sunset directions, but are not
the same. And just so you don't think I'm disagreeing with you, your
argument applies just as well to this as it does to sunrise/sunset
positions.

Re: Vernal Equinox Re: day 3000 of 3rd

On 2009.03.20, at 15:54 , Victor Engel wrote:

True. I wasn't talking about sunrise/sunset direction, though, butmaximum elevation of the sun above the horizon -- zenith. Thenorthernmost zenith occurs at the northern solstice. The southernmostzenith occurs at the southern solstice. My assertion is that theequinox occurs at and angle that is midway between those two angles.These angles are related to sunrise and sunset directions, but are notthe same. And just so you don't think I'm disagreeing with you, yourargument applies just as well to this as it does to sunrise/sunsetpositions.

Irv replies: You could use a gnomon to find the maximum and minimum solar declinations, but the observer would have to be watching during the solar culmination at mid-day (I suppose this is no more onerous that having to be watching at the moment of sunrise or sunset). Sun would only actually be at the maximum or minimum declination at that time if that moment at that locale also happens to coincide with the moment of the solstice, which will rarely be the case. Also, due to the 1/2° diameter of the solar disk the shadow of the gnomon is not sharp, so one would have to take care to find the mid-point of the shadow. It is true that at mid-day the effect of atmospheric refraction ought to be negligible except at high terrestrial latitudes when Sun is very low in altitude at the opposite solstice.

You could say that it is an equinox when the end of the gnomon's shadow at mid-day is half-way in-between those two extremes, but you don't need that because if the sundial is properly set up the end of the gnomon's shadow follows a straight-line path on the day of the equinox, instead of its usual hyperbolic path (of course this won't work with the equatorial sundials that I wrote about previously in this thread -- for them on the day of the equinox the gnomon shadow would be centered on the dial inner rim, with equal intensity shadows on the upper and lower dial surfaces).

Also, the discussion concerned the origin of the word "equinox" (Latin for equal night), which clearly has nothing to do with sunrise/set direction or the solar declination at mid-day. That leaves sundial measurement of the length of the day, which would be very close to 12 hours on the day of the equinox.

Re: Vernal Equinox Re: day 3000 of 3rd

> On 2009.03.20, at 15:54 , Victor Engel wrote:
>> True. I wasn't talking about sunrise/sunset direction, though, but
>> maximum elevation of the sun above the horizon -- zenith. The
>> northernmost zenith occurs at the northern solstice. The southernmost
>> zenith occurs at the southern solstice. My assertion is that the
>> equinox occurs at and angle that is midway between those two angles.
>> These angles are related to sunrise and sunset directions, but are not
>> the same. And just so you don't think I'm disagreeing with you, your
>> argument applies just as well to this as it does to sunrise/sunset
>> positions.
>
> Irv replies: You could use a gnomon to find the maximum and minimum
> solar declinations, but the observer would have to be watching during
> the solar culmination at mid-day (I suppose this is no more onerous
> that having to be watching at the moment of sunrise or sunset). Sun
> would only actually be at the maximum or minimum declination at that
> time if that moment at that locale also happens to coincide with the
> moment of the solstice, which will rarely be the case. Also, due to
> the 1/2° diameter of the solar disk the shadow of the gnomon is not
> sharp, so one would have to take care to find the mid-point of the
> shadow. It is true that at mid-day the effect of atmospheric
> refraction ought to be negligible except at high terrestrial latitudes
> when Sun is very low in altitude at the opposite solstice.
>
> You could say that it is an equinox when the end of the gnomon's
> shadow at mid-day is half-way in-between those two extremes, but you
> don't need that because if the sundial is properly set up the end of
> the gnomon's shadow follows a straight-line path on the day of the
> equinox, instead of its usual hyperbolic path (of course this won't
> work with the equatorial sundials that I wrote about previously in
> this thread -- for them on the day of the equinox the gnomon shadow
> would be centered on the dial inner rim, with equal intensity shadows
> on the upper and lower dial surfaces).
>
> Also, the discussion concerned the origin of the word "equinox" (Latin
> for equal night), which clearly has nothing to do with sunrise/set
> direction or the solar declination at mid-day. That leaves sundial
> measurement of the length of the day, which would be very close to 12
> hours on the day of the equinox.
>
> -- Irv Bromberg, Toronto, Canada
>
> <http://www.sym454.org/seasons/>

Re: Vernal Equinox Re: day 3000 of 3rd

Yes, the Sun and Moon are proper names. A man named Mundilfari had a son named Moon and a daughter named Sun. When Odin was creating the universe, He placed them in chariots to guide the orbs around the sky. Note that Sun is feminine and Moon is masculine. The names are similar throughout the Germanic languages, which of course includes English.